<dom-module id="shared-style">
  <template>
    <style>
      :root {
        --import-var: 3px solid orange;
      }
    </style>
  </template>
</dom-module>

<dom-module id="shared-style2">
  <template>
    <style>
      .zazz {
        border: 16px solid orange;
      }
    </style>
  </template>
</dom-module>

<link rel="import" href="sub/style-import.html">

<style is="custom-style" include="shared-style style-import">
  :root {

    --import-mixin: {
      border: 4px solid blue;
    };

    padding: 10px;
  }
</style>
